This study is designed to address questions regarding the possible association between the intake of various dietary components and cancer of the breast and large bowel, as well as other disease outcomes. This is to be done by taking advantage of an existing prospective study of risk factors for breast cancer in 121,000 women who complete a mail questionnaire on a biennial basis. The questionnaire is designed to provide relative scores for individuals on: intake of animal fat, vegetable fat, cholesterol, potein, fiber, Vitamin A, and "trans" fatty acids. Data on potential confounding factors, including physical activity, for risk of breast cancer and large bowel cancer are being collected and will be controlled by multiple logistic analyses. To validate the questionnaire, 200 subjects will complete detailed 7-day food use diaries four times over a 1-year period. Blood specimens will be assessed for carotene and vitamin A levels. Outcome measure will include both fatal and non-fatal cancer incidence rates. Reported cases of cancer will be documented by obtaining copies of hospital records and causes of death will be obtained from death certificates as well as hospital records.